1. Field of the Invention
This invention relates to a method and apparatus for improving aircraft safety. More specifically, it relates to an apparatus and method for preventing combustion in aircraft fuel tanks and cargo spaces by supplying inert gas using turbocharged engine bleed air.
2. Description of the Related Art
Military aircraft have used On-board Inert Gas Generating Systems (OBIGGS) for some years to protect against fuel tank explosions due to undesired phenomena, such as penetration from small arms fire. Military aircraft are not the only aircraft that would benefit from OBIGGS. For example, investigations into the cause of recent air disasters have concluded that unknown sources may be responsible for fuel tank ignition and explosion. Subsequently, OBIGGS has been evaluated as a way to protect commercial aircraft against such fuel tank explosions started by unknown ignition sources.
OBIGGS protects against fuel tank explosions by replacing the potentially explosive fuel/air mixture above the fuel in the tanks (the ullage) with an inert gas (usually nitrogen—N2). The nitrogen is generated by separating oxygen from local, ambient air and pumping the inert product into the tanks.
In previous applications, OBIGGS has proved relatively unreliable, heavy, and costly for both initial acquisition and operation in aircraft. Furthermore, military aircraft systems often have the strict requirements that derive from military flight profiles that include high-rate descent from high-altitude flight. Applications of OBIGGS to commercial aircraft would benefit by considering the fact that a typical flight profile for the commercial application has a less demanding requirement for the system because commercial aircraft do not operate at the same flight profiles of military aircraft.
Thus, there is a need for a gas generation and inerting system that minimizes the quantity and complexity of sub-components (particularly moving parts). The system should also consider a typical commercial aircraft flight profile and take advantage of the reduced descent rates (compared to military aircraft).